Palm kernel shell (PKS) was incorporated with polylactic acid (PLA) using a solution casting method to produce PLA/PKS biocomposite films. The effects of filler content and butyl methacrylate on the mechanical properties, morphological properties, and thermal properties of PLA/PKS biocomposite films were studied. The addition of PKS into the PLA matrix decreased the tensile strength and elongation at break of PLA/PKS biocomposite films with increasing filler content. In contrast, the modulus of elasticity of the biocomposite films increased. The use of butyl methacrylate as a chemical modification for PKS enhanced the interfacial adhesion and wettability of PKS inside the PLA matrix. This effect was confirmed by the increase in tensile strength, modulus of elasticity, and thermal stability of the biocomposite films. Moreover, scanning electron microscopy showed that there was better interfacial interaction between the filler and the PLA matrix.